This paper describes the application of a novel approach in electric field modulation spectroscopy, the differential photoreflectance (DPR), to study buried GaAs/AlGaAs heterostructures. We show that in most complicated device structures. DPR can provide selective photoreflectance (PR) response from layers buried within thin multilayer structures. Such responses are often superimposed on one another in conventional PR measurements. DPR measurement is achieved through alternative modulations from two laser pumps with different penetration depths, so that the modulation has a gradient with respect to the depth within the sample. The application of this technique is demonstrated for a two-dimensional electron gas (2DEG) of a modulation doped heterojunction in comparison with conventional PR. In one case the heterojunction of interest was buried under two highly doped GaAs and AlGaAs layers 40 nm thick. We show that this heterojunction is barely distinguishable in a PR measurement. Nevertheless, at room temperature DPR shows distinct peaked signals that correspond to the previously reported PR from a two-dimensional electron gas.